Mukaiyama Aldol reactions are known. Dialkyl acetals are known to be substituted by Mukaiyama aldol reactions with silyl enol ethers or silyl ketene acetals affording β-alkoxy ketones or esters (K. Saigo, M. Osaki, T. Mukaiyama, Chem. Lett. 1976, 769-770; T. Mukaiyama, M. Murakami, Synthesis 1987, 1043-1054; S. Kano, T. Yokomatsu, H. Iwasawa, S. Shibuya, Chem. Lett. 1987, 1531-1534; M. A. Graham, A. H. Wadsworth, M. Thornten-Pett, B.Carrozzini, G. L. Cascarano, C. M. Rayner, Tetrahedron Lett. 2001, 42, 2865-2868; M. A. Graham, A. H. Wadsworth, M. Thornten-Pett, B.Carrozzini, G. L. Cascarano, C. M. Rayner, Org. Biomol. Chem. 2003, 1, 834-849).
Surprisingly, it has now been found that N-benzyl-protected dialkyl acetal derivatives undergo desired aldol reaction with high diastereoselectivity using a Mukaiyama aldol reaction.